The Prophet (Sallalaahu ‘alaihi wa sallam) did not used to pray anything before the ‘Asr prayer. Rather he would pray either two rak’ahs before Dhuhr or four rak’ahs after it. He would pray two rak’ahs after Maghrib and likewise after ‘Ishaa he would pray two rak’ahs as well as two rak’ahs before Fajr. As for before ‘Asr and before Maghrib and before ‘Ishaa; then he would not pray anything.
However; it is established from him in the ((Saheeh)) that he said: ((There is between every two adhaans a prayer)), then he said on the third time: ((For whomsoever wishes)) – out of dislike that the people should take it as a Sunnah. So whosoever wishes to pray willingly (voluntarily) before ‘Asr, then that is good, but he should not take that as a Sunnah, and Allaah knows best.